Cradle-robbing teacher Mary Kay Letourneau said she was only joking when she threatened to castrate her teen lover if he dated other women.

The jailed Seattle teacher – convicted of statutory rape for having an affair with her former student – told “Inside Edition” she was just kidding when she threatened 15-year-old Vili Fualaau with “automatic castration” if she caught him “touching or talking” to another woman.

The teen, who started sleeping with his homeroom teacher when he was 12 and in sixth grade, showed five bizarre love letters on the show.

He claimed they were written by his jailed lover, with whom he has fathered two children.

“We are separated,” Letourneau said on the show during in a telephone interview from the Washington Correctional Center for Women. “Anyone in a relationship is going to express themselves emotionally about that separation.”

“Sometimes that comes out in anger, sometimes there is sarcasm … There are a lot of emotions I shouldn’t have to explain.”

Letourneau, 37, who is serving a seven-year sentence and is forbidden to contact her boy-toy lover, denied sending the letters.

She said she has no idea how he received them.

“It helps me to write as if I’m talking to him and I do send material out, but not for the purpose of him receiving it,” Letourneau said.